1. Field of the Invention
The present invention relates to a battery having a collecting structure and a sealing structure that are novel and allow increase of output and capacity, and a method for manufacturing such battery in a suitable manner.
2. Description of the Related Art
In recent years, it has been advanced rapidly to make electronic devices such as audio-video equipment and a personal computer or mobile communication equipment portable and/or cordless. As a driving power source of these electronic devices, an aqueous battery such as a nickel-cadmium battery or nickel metal hydride battery was typically used conventionally. However, the aqueous battery has been recently replaced with a non-aqueous electrolyte battery that can be charged quickly and is high in both volume energy density and weight energy density. As a typical non-aqueous electrolyte battery, a lithium rechargeable battery is known. On the other hand, the nickel-cadmium battery and the nickel metal hydride battery mentioned above have been specialized in applications requiring large load characteristics, such as a driving power source of a cordless power tool or an electric vehicle. Thus, the nickel-cadmium battery and the nickel metal hydride battery are required to have larger current discharging characteristics.
As a conventional battery that can be used in large-current discharging application, a battery having a structure shown in FIG. 19 is known. This battery (hereinafter, referred to as a first conventional battery) includes an electrode plate group 50 accommodated in a metal battery case 51 that is a cylinder having a bottom. The electrode plate group 50 includes a strip-shaped positive electrode plate and a strip-shaped negative electrode plate (both not shown) that are overlapped with a separator (not shown) interposed therebetween and are wound spirally. A structure for collecting an output from and an input to the positive and negative electrode plates is formed as follows, here the structure being suitable for large-current discharge. The electrode plate group 50 is arranged in such a manner that an end (not shown) of the positive electrode plate protrudes above the electrode plate group 50 and an end (not shown) of the negative electrode plate protrudes below the electrode plate group 50. To the end of the positive electrode plate, a substantially circular disk-like positive collector 52 is welded at a plurality of positions. To that positive collector 52, one end 53a of a positive lead 53 is welded by resistance welding. The other end 53b of the positive lead 53 is welded to a filter portion 57 of a sealing member 54 by resistance welding. Furthermore, a negative collector (not shown) is welded to the end of the negative electrode plate by resistance welding, and a negative collecting piece (not shown) of the negative collector, which is like a tongue shape, is welded to the bottom of the battery case 51 by resistance welding.
The sealing member 54 includes the filter portion 57, a cap-shaped positive terminal 58 and a safety vent body 59 interposed between the filter portion 57 and the positive terminal 58, all of which are integrated to form one unit. In the sealing member 54, the safety vent body 59, while being compressed, closes a vent opening 57a of the filter portion 57. When a pressure inside the battery has reached or exceeded a set pressure that is set by the safety vent body 59, the safety vent body 59 changes its shape so as to open the vent opening 57a, thereby allowing gas to escape to the outside through the vent opening 57a to decrease its internal pressure. Then, the shape of the safety vent body 59 returns to its original shape, thereby closing the vent opening 57a. 
In an outer circumferential surface of the battery case 51, an annular groove 51a is provided. The annular groove 51a forms an annular supporting portion 51b in such a manner that the supporting portion 51b bulges inward. The sealing member 54 is supported by the supporting portion 51b with an insulation gasket 60 interposed therebetween. In addition, the peripheral edge portion of the filter portion 57 is held and secured by upper and lower opening edge portions of the battery case 51, that have been caulked inward, from above and beneath, with the insulation gasket 60 interposed therebetween, so that the sealing member 54 is secured. Moreover, a ring-like upper insulation plate 61 is provided between the upper end of the peripheral edge portion of the electrode plate group 50 and the lower surface of the annular supporting portion 51b. This ring-like upper insulation plate 61 secures the electrode plate group 50 within the battery case 51 so as not to allow any movement of the electrode plate group 50 and also prevents short-circuit between the electrode plate group 50 and the annular supporting portion 51b that may occur when they come into contact with each other.
In the above battery, the positive lead 53 is bent at two positions to have a substantially Z-shape when seen from the side thereof, in order to prevent short-circuit between the positive lead 53 and the annular supporting portion 51b of the battery case 51 that may occur when the positive lead 53 comes into contact with the annular supporting portion 51b. Aside from this, a battery shown in FIG. 20 (hereinafter, referred to as a second conventional battery) includes the positive lead 53 that is bent at one position. In FIG. 20, the components that are the same as or similar to those in FIG. 19 are labeled with the same reference numerals, and the redundant description is omitted.
The second conventional battery is fabricated in the following assembly processes. As shown in FIGS. 21A and 21B, the electrode plate group 50 is inserted into the battery case 51 and thereafter the positive collector 52 and the negative collector (not shown) are welded to the positive and negative electrode plates, respectively. Then, the ring-like upper insulation plate 61 is inserted into the battery case 51 and is placed on the positive collector 52. Subsequently, the annular groove 51a is formed at a predetermined portion on the outer circumferential surface of the battery case 51. Then, a predetermined portion 53a at one end of the positive lead 53 is welded to a portion of the positive collector 52 that is located on one side (on right side in FIG. 21A) of a central gap of the electrode plate group 50. Then, the positive lead 53 is bent at a portion near the welded portion perpendicularly and upward, so that the positive lead 53 stands to have a substantially L-shape and protrudes from the opening of the battery case 51. Thereafter, the filter portion 57 of the sealing member 54 that has been assembled in advance is welded to a predetermined portion 53b at the other end of the positive lead 53. The reason why the positive lead 53 is bent to stand up above the central portion of the electrode plate group 50 is to achieve smooth insertion of the sealing member 54 into the opening of the battery case 51 having the annular supporting portion 51b without bringing the lower end of the filter portion 57 of the sealing member 54 into contact with the annular supporting portion 51b. 
Subsequently, the positive lead 53 is bent to be curved so as to rotate the sealing member 54 as shown with an arrow in FIG. 21A, thereby arranging the sealing member 54 in a relative arrangement that enables insertion of the sealing member 54 into the opening of the battery case 51. Then, the sealing member 54 is inserted into the battery case 51 and the peripheral edge of the filter portion 57 of the sealing member 54 is placed on the annular supporting portion 51b of the battery case 51 with the insulation gasket 60 interposed therebetween. At this time, the other end 53b of the positive lead 53 is arranged above the gap of the center of the electrode plate group 50. In this state, an opening edge portion of the battery case 51 is caulked inward. Thus, the opening edge portion compresses the insulation gasket 60, so that the peripheral edge portion of the filter portion 57 is held securely.
In most conventional batteries, the opening of the battery case 51 is sealed with the sealing member 54, as shown in FIG. 19, and thereafter a pressure is applied to the battery case 51 in a direction along the axis of the battery case 51 (vertical direction of the battery case 51) so as to press the sealing member 54 down toward the inside of the battery case 51 while flattening out the annular groove 51a. As a result, the sealing member 54 securely presses the electrode plate 50 by means of the upper insulation plate 61 with the positive lead 53 interposed therebetween. During this application of the pressure, the positive lead 53 is deformed so as to be folded. However, the vent opening 57a of the sealing member 54 may be closed by a portion of the positive lead 53, which is located at the center of the electrode plate group 50, because of variation of the position of the positive lead 53 at which the positive lead 53 is welded to the filter portion 57.
In order to overcome the above drawback, other batteries have been conventionally proposed. One of those batteries has a positive lead portion formed integrally with a positive collector portion with a folded portion positioned in therebetween. In this battery (hereinafter referred to as a third conventional battery), the conventional positive collector and positive lead are formed integrally with each other. The positive lead portion has a horseshoe shape with a U-shaped notch that is to fit into a ring-like projection projecting from the vent opening of the sealing member. See Japanese Utility Model Laid-Open Publication No. Sho 58-74768, for example.
Moreover, still another conventional battery (hereinafter, referred to as a fourth conventional battery) is fabricated in a process shown in FIG. 22 (see Japanese Patent Laid-Open Publication No. 2001-155712, for example). More specifically, the positive lead 53 is welded to a substantially central portion of the positive collector 52 at its one end 53a. Then, the positive lead 53 is bent upward at a portion near the welded portion perpendicularly so as to stand like an L-shape and is positioned in such a manner that a gas escape hole 53d provided at its other end portion is in agreement with the vent opening 57a of the filter portion 57 of the sealing member 54. In this state, portions 53b and 53c near the gas escape hole 53d are welded to the filter portion 57. Subsequently, the sealing member 54 is inserted into the opening of the battery case 51 while the positive lead 53 is bent, and is then placed on the annular supporting portion 51b with the insulation gasket 60 therebetween. Finally, the opening of the battery case 51 is caulked toward the inside of the battery case 51. Please note that the components in FIG. 22 that are the same as or similar to those in FIGS. 21A and 21B are labeled with the same reference numerals in order to omit the redundant description.
Moreover, still another battery assembled in a process shown in FIG. 23 has been conventionally proposed, as described in Japanese Patent Laid-Open Publication No. 2001-256935, for example. In FIG. 23, the components that are the same as or similar to those in FIG. 21A are labeled with the same reference numerals. This battery (hereinafter, referred to as a fifth conventional battery) is fabricated as follows. In welding of the positive lead 53 and the sealing member 54, firstly, one end of the positive lead 53 is welded to the peripheral end portion of the positive collector 52. Then, the filter portion 57 of the sealing member 54 arranged vertically above that welded portion of the positive lead 53 is welded to the other end of the positive lead 53. The sealing member 54 is then inserted into the opening of the battery case 51 while being rotated as shown with an arrow in FIG. 23 so as to be arranged horizontally. In this battery, one end of the positive lead 53 is welded to the peripheral end portion of the positive collector 52. Thus, the positive lead 53 does not exist above the gap at the center of the electrode plate group 50 when the annular groove (not shown) is flattened out after the sealing member 54 closed the opening of the batter case 51. Therefore, the vent opening 57a of the filter portion 57 cannot be closed by the positive lead 53.
Attaching the sealing member 54 to the insulation gasket 60 is performed in accordance with a procedure shown in FIGS. 24A through 24C (see Japanese Patent Laid-Open Publication No. Hei 6-267516, for example). More specifically, the sealing member 54 is inserted into the insulation gasket 60 at an angle, as shown in FIG. 24A, and one end of the filter portion 57 of the sealing member 54 is then brought into contact with a bottom surface of the insulation gasket 60, as shown in FIG. 24B. Finally, the other end of the filter portion 57 placed on the upper end portion of the insulation gasket 60 is pressed down so as to cause slight deformation of the insulation gasket 60 to the outside and is further pressed down along the inner side face of the insulation gasket 60. In this manner, the insertion of the sealing member 54 into the insulation gasket 60 is performed.
However, in the first conventional battery, the positive lead 53 is bent to have a substantially Z-shape, as shown in FIG. 19. Thus, a collecting distance increases as the length of the positive lead 53 increases. In addition, it is necessary to make the positive lead 53 in the first conventional battery thinner because the positive lead 53 has to be bent twice. This increases the internal resistance of the battery and acts as a factor of disturbing large-current discharge characteristics. Moreover, the welded portions of the long thin positive lead 53 and the sealing member 54 may come off when the battery receives strong impact or vibration and the electrode plate 50 is moved. This decreases vibration resistance or impact resistance of the battery.
The second conventional battery has an advantage that the length of the positive lead 53 can be made slightly shorter, as compared with the first conventional battery. However, since there is the annular supporting portion 51b for pressing the electrode plate group 50 and supporting the sealing member 54, and the filter portion 57 of the sealing member 54 and the upper end of the electrode plate group 50 are arranged above and below the annular supporting portion 51b, respectively, the filter portion 57 and the upper end of the electrode plate group 50 are arranged away from each other by a relatively large distance. Thus, the positive lead 53 has to have the length corresponding to the above large distance. This prevents the reduction of the internal resistance of the battery and the improvement of the large-current discharging characteristics. Moreover, in the second conventional battery, the sealing member 54 has to be arranged at the central portion of the battery case 51, as shown in FIG. 21A, when being bonded to the positive lead 53 that is bent to be L-shaped and thus erected. Thus, when electrolyte is injected into the battery case 51 after the bonding of the sealing member 54 to the positive lead 53, it is necessary to bend the positive lead 53 to the right from the state shown in FIG. 21A so as to move the sealing member 54 away from the gas escape hole 52a of the positive collector 52, then move the positive lead 53 back to the state shown in FIG. 21A after the injection of the electrolyte, and finally rotate the sealing member 54 in the direction shown with the arrow in FIG. 21A. Therefore, the increase of number of unnecessary work decreases productivity.
The third conventional battery also has problems mentioned below. When the horseshoe-shaped notch of the positive lead portion is positioned at the ring-like projection of the sealing member, secure positioning cannot be achieved unless the innermost portion of the notch is brought into contact with the ring-like projection. During the positioning, even a small misalignment causes variations of positions at which spot welding is performed or defective welding. Moreover, since the positive lead has a horseshoe shape, welded portions of spot welding directly receive load when vibration is applied to the battery. Thus, the welded portions may come off easily.
In the fourth conventional battery, welding of the positive lead 53 and the sealing member 54 to each other is performed while the sealing member 54 is displaced from the center of the battery case 51 toward the side of bending of the positive lead 53. Thus, there is an advantage that electrolyte can be injected without moving the sealing member 54 after the welding of the positive lead 53 and the sealing member 54. However, since the fourth conventional battery also has the annular groove 51a in the battery case 51, the filter portion 57 of the sealing member 54 and the upper end of the electrode plate group 50, that are arranged above and below the annular supporting portion 51b, respectively, are away from each other by a relatively large distance. Thus, the positive lead 53 has to have a length corresponding to the above large distance, preventing reduction of the internal resistance of the battery.
Furthermore, in the fifth conventional battery, the peripheral edge portion of the sealing member 54 inevitably comes into contact with the edge of the opening of the battery case 51. Therefore, it is hard to put the fifth conventional battery into practical use.